Activation of 125I‐Factor IX and 125I‐Factor X: Effect of Tissue Factor and Factor VII, Factor Xa and Thrombin

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Abstract
Activation of [human] Factor [F] IX and FX was studied by adding 125I-FIX or 125I-FX to reaction mixtures and quantitating cleavage products by reduced sodium dodecylsulfate gel electophoresis. Thrombin failed to activate FIX or X; FXa produced insignificant amounts of cleavage products of both factors. The reaction product of tissue factor and FVII cleaved large amounts of FIX and FX in purified systems and in plasma. In incubation mixtures of plasma containing added 125I-FIX or 125I-FX, tissue factor and Ca2+ ions: the percentage of total radioactivity in the heavy chain peak of 125I-IXa and the heavy chain peak of 125I-Xa increased at a similar rate. When the tissue factor was diluted, similar curves were obtained for percent cleavage of 125I-FIX and percent cleavage of 125I-FX plotted against tissue factor concentration. These findings support the hypothesis that activation of FIX by the tissue factor-FVII reaction product represents a physiologically significant step in normal hemostasis.